In a diesel engine comprising an exhaust gas recirculation system (EGR system), an exhaust gas recirculation amount (EGR amount) is controlled based for example on an amount of fuel injected in the engine.
Tokkai Sho 63-230994 published by the Japanese Patent Office in 1988 discloses a fuel injection control device having a function to estimate a real amount of fuel injected in the engine.
A target fuel injection amount which this device applies for the control of fuel injection amount is generally determined based on the load and rotation speed of the engine. To perform control of the fuel injection amount, the opening period of a fuel injection nozzle is increased or decreased so that a real injection amount coincides with the target injection amount. However, the target injection amount and real injection amount may not coincide due to variation of the performance of a fuel injection pump. Hence when the EGR is controlled based on the target injection amount, there is a possibility that the EGR amount will be out of a preferred range due to the difference between the target injection amount and real injection amount, and cause increased generation of smoke.
In this context in the aforesaid control device, the EGR amount is controlled taking account of the difference between a preset target fuel injection amount corresponding to a predetermined target idle rotation speed and a real fuel injection amount in a state when this target idle rotation speed is actually obtained, i.e. a fuel injection amount error.
In this way, the effect of dispersion in the fuel injection pump performance on EGR amount control is eliminated.
Such control is not limited to the control of EGR amount, and may be applied also to control of a swirl control-valve or to the control of a fuel injection period.
However when a load due to air conditioner or power steering for example is exerted on the engine, the fuel amount required to maintain the same rotation speed also varies, and as these load variations are not reflected in the calculation of fuel injection amount error, the EGR amount control precision also falls when the load deviates from standard conditions.
Moreover an error of injection amount in the idle running state is also largely subject to a difference in the initial lift amount of the fuel injection nozzle due to manufacturing errors or time-dependent changes, or to a difference of the nozzle opening pressure. If this initial lift amount or nozzle opening pressure is not considered in calculating injection amount error under the aforesaid load, a suitable correction amount is not obtained under all running conditions.